Absorption refrigeration systems, methods, and absorbent compositions



June 1958 R. J. MODAHL ET AL 3,388,557

ABSORPTION REFRIGERATION SYSTEMS, METHODS, AND

ABSORBENT COMPOSITIONS Filed April 3, 1967 6 Sheets-Sheet l Ea-AHHHHHHHH63 mun Ilh

mum

INVENTORS ROBERT J. MODAHL PAUL J. LYNCH ATTORNEYS June 18, 1968 R. JMODAHL. ET AL 3,

ABSORPTION REFRIGERATION SYSTEMS, METHODS, AND

ABSORBENT COMPOSITIONS 6 Sheets-Sheet 2 Filed April 1967 INVENTORSROBERT J. MODAHL PAUL J.LYNCH BYM$M ATTORNEYS June 18, 1968 R. J MODAHLET AL 3,338,557

ABSORPTION REFRIGERATION SYSTEMS, METHOD AND ABSORBENT COMPOSITIONSFiled April 1967 6 Sheets-Sheet 3 42 Fig. 4

INVENTORS ROBERT J. MODAHL PAUL J- LYNCH mam ATTORNEYS June 18, 1968 R.J. MODAHL ET AL 3,

ABSORPTION REFRIGERATION SYSTEMS, METHODS, AND

ABSORBENT COMPOSITIONS 6 Sheets-Sheet 4 Filed April 5, 1967 L T ww HY LT168 WW YY Y .0 filo- BM L 7 r/ I4 s 1 II In A I I E I m "L L /I M n O MY L 8 A u r T S 5 Y 6 R C TY 88 um u r SW M TV: I m n L a E LN ML S Y RC O O O O O O 5 2 6 6 4 2 I 2 3 I T E M P E R A T U R E roscnsss F.)

A T TORN EYS June 18, 1968 AND R. J. MODAHL. ET AL ABSORPTIONREFRIGERATION SYSTEMS,

ABSORBENT COMPOSITIONS METHODS Filed April 5, 1967 6 Sheets-Sheet 5 I Ia o I V I I 7 o f "7 I s o I 5 o I I LEGEND 1 I40 I m I HANDBOOK OF 0:30 I CHEMISTRY a PHYSICS, D I 36 TH EDITION, PAGE F I I60! I954 55 I20 II: 1 APPLICANTS Lu N o l INTERNATIONAL 5 CRITICAL TABLES 4, III [1V233,(I928) F l s o so 62 e4 66 68 7o 72 74 76 7a 60 82 W E l G H T LI' IFIG. 7

IN VENTORS R OBER T J. MODAHL PAUL J. LYNCH 621% QMM A T TORN EYS 3,388,55 7 AND June 18, 1968 R. MODAHL ET AL REFRIGERATION SYSTEMS,

ABSORPTION METHODS ABSORBENT COMPOSITIONS 6 Sheets-Sheet 6 Filed April1967 m. me ks E on:

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A T TORNEYS United States Patent 7 Claims. or. 62-412) ABSTRACT OF THEDISCLGSURE Absorption refrigeration systems and processes employing anabsorbent comprised of lithium iodide, ethylene glycol and water foroperation With a high temperature heat sink such as air.

This application is a continuation in part of copending application Ser.No. 404,732 filed Oct. 19, 1964, now abandoned.

The present invention relates to the art of heating and cooling andparticularly to air conditioning employing a heat operated absorptionrefrigeration system. More particularly this invention relates toabsorption refrigeration systems and processes and to absorbentrefrigerant compositions for operation with high temperature heat sinks.

Absorbent refrigeration systems normally require the absorbent materialto remain in liquid form throughout the cycle of operation and arefrigerant material adapted to have a liquid phase and vapor phase.

The usual absorption refrigeration system has a generator in which theabsorbent, diluted with absorbed refrigerant, is heated to boil off someof the refrigerant. The refrigerant vapor flows to a condenser in whichthe refrigerant vapor is condensed to a liquid by heat exchange with anexternal cooling fluid maintained at a suitable temperature by a heatsink. The liquefied refrigerant flows through a throttle valve orequivalent regulating device to an evaporator which is kept at a reducedpressure so that the liquid refrigerant boils at a relatively lowtemperature and produces refrigeration. In the evaporator, the coldrefrigerant absorbs heat from an external fluid which is circulatedthrough the evaporator and is thereby cooled to substantially theevaporator temperature. This cooled external fluid is circulated to arefrigeration load.

The vaporized refrigerant from the evaporator flows to an absorber whereit is absorbed by concentrated absorbent supplied from the generator.The absorption of refrigerant vapor maintains the low pressure in theevaporator. Since the concentrated absorbent was heated in the generatorand the act of absorption also generates heat, the absorber must becooled to suitable operating temperature by heat exchange with anexternal cooling fluid, the heat sink. From the absorber, the dilutedabsorbent passes to the generator to be concentrated by heating theabsorbent to boil off some of the refrigerant and thus repeat the cycle.A pump is often used in the system to help return the diluted absorbentto the generator. Also, the diluted absorbent passing to the generatorfrom the absorber is often put in heat exchange with the concentratedabsorbent passing from the generator to the absorber. Absorptionrefrigeration systems are closed, and made as leakproof as possible toprevent the entrance of air or other external materials into the systemor the escape of the operating materials from the system.

At the present time, absorption refrigeration systems for comfort airconditioning usually use an aqueous solution of lithium bromide as anabsorbent and Water as a refrigerant. Such systems When used for comfortair condition- Patented June 18, 1968 ing normally require maintainingin the evaporator a temperature of about 40 F. To maintain suchtemperature and low pressure in the evaporator, the concentration,temperature, and absorptive ability of the absorbent solution in theabsorber must be suflicient to maintain a vapor pressure over theabsorbent solution which is less than the vapor pressure of Water atsuch temperature and pressure.

Currently, most large capacity absorption refrigeration systems forcomfort air conditioning, in addition to using Water as the refrigerantand an aqueous solution of lithium bromide as the absorbent, maintainthe condenser and absorber at suitable operating temperatures by heatexchange with external cooling water. This cooling water acts as anintermediate heat transfer fluid and rejects heat to an air sink bymeans of a cooling tower. This intermediate heat transfer fluid isusually supplied to the absorber at a temperature of about F.

With a higher temperature heat transfer fluid, the concentration ofabsorbent in the absorber must be greater in order for the highertemperature solution to have a vapor pressure less than that of Water at40 F. For intermediate heat transfer fluids having temperatures of aboutF., the risk of crystallization is so great that reliable operation ofthe system cannot be assured.

It has long been desired to reject heat from an absorption cycleemploying an aqueous solution of a salt as an absorbent and Water as arefrigerant by heat exchange directly to air. But this has not beenpractical with the absorbent salt solutions presently available. Forsuch an air cooled system, ambient air temperatures of 95 to F. areassumed for design purposes. For purposes of explanation, an ambient airtemperature of 110 F. 'will be assumed. In order to keep the amount ofheat transfer surface within economical limits, it is necessary that theprocess be operated at 20 higher than the heat sink or at F. under theassumed condition of ambient air at 110 F. Furthermore, at suchtemperatures, the absorbent at the required concentration must becapable of remaining a liquid free from crystals and of having enoughabsorbing power to maintain the low vapor pressure required in theevaporator to keep the evaporator temperature at about 40 F.

Except for the system and methods of our US. Patent No. 3,296,814, tothe best of our knowledge, no practical absorption system or process wasknown which could be used with Water as a refrigerant to permit heatrejection directly to air, in spite of the fact that a vast number ofabsorbent-refrigerant combinations had been suggested and some tested bythe refrigeration industry over a considerable period and in spite ofthe fact that the gas industry for many years had been assisting andurging the refrigeration industry to find such a combination .(See, forexample, the articles entitled, Refrigerants and Absorbents, by Dr. W.R. Hainsworth, parts I and II of which are published in the August andSeptember, 1944 issues of Refrigerating Engineering at pp. 97 thru 1 00,and pp. 201 thru 205 of that publication. See also, Research Bulletin14, entitled, The Absorption Cooling Process, published in 1957 by theInstitute of Gas Technology and sponsored by The General ResearchPlanning Committee of the American Gas Association.)

Accordingly, it is a principal object of this invention to provideabsorption refrigeration systems and processes for operation With hightemperature heat sinks such as air.

It is a further object of this invention to provide arefrigerant-absorbent combination which permits operation of anabsorption-refrigeration system and process at an evaporator temperatureof about 40 F. and at absorber temperatures above about 130 F.

It is a further object of this invention to provide a refrigerantabsorbent composition which Will not be subject to crystallization Whenthe absorber is cooled by a it relatively high temperature heat sinksuch as is encountered in a system which is directly cooled by air.

It is another object of the invention to provide an absorbentcomposition which is stable, and non-toxic, and which has a low vaporpressure, and low viscosity at operating temperatures.

It is another object of this invention to provide an improved absorbentcomposition comprising an aqueous solution of lithium iodide andethylene glycol, wherein the weight of lithium iodide is about 2.5 to 13times the weight of ethylene glycol.

It is another object of this invention to provide an improved absorbentcomposition comprising lithium iodide and ethylene glycol for use withwater as a refrigerant.

It is a further object of this invention to provide an absorptionrefrigeration system employing in combination an absorptionrefrigeration apparatus with a novel refrigerant absorbent composition.

It is also an object of the present invention to provide a novel processfor producing refrigeration employing a refrigerant absorbentcomposition of the present invention.

Other objects and advantages of this invention will be apparent as thespecification proceeds to describe the invention with reference to theaccompanying drawings in which:

FIGURE 1 shows more or less diagrammatically a system incorporating oneembodiment of an absorption refrigeration apparatus eminentlysatisfactory for use in our invention and showing operation during thecooling cycle;

FIGURE 2 is a perspective view of the apparatus referred to in FIGURE 1and showing the arrangement of the components of the apparatus withportions of the cabinet broken away to more clearly show the interiorconstruction;

FIGURE 3 is an enlarged sectional view of the evaporator taken on line33 of FIGURE 1;

FIGURE 4 is an enlarged vertical sectional view of the evaporator takenon line 4-4 of FIGURE 3;

FIGURE 3 is a diagram showing the controls of our invention;

FIGURE 6 shows a crystallization curve and some vapor pressure curvesfor certain of our improved absorbent compositions and for certaincompositions of lithium bromide and water (LiBr-H O);

FIGURE 7 shows crystallization curves illustrating Weight percentagainst temperature for lithium iodide and water, two of the curvesbeing made for prior published data, and one of them made from dataobtained in our tests;

FIGURE 8 shows isothermal crystallization curves for compositions oflithium bromide, ethylene glycol and water (LiBr-C H -O -H O) made fromdata obtained in our tests;

FIGURE 9 shows isothermal crystallization curves for compositions oflithium iodide, ethylene glycol and water (Li-C H O -H O) made from dataobtained in our tests.

Referring now to FIGURE 1, one form of absorption refrigerationapparatus which is highly satisfactory for use in the systems of thepresent invention is shown applied to an operation having a coolingcycle for cooling air in the summer and having a heating cycle forheating air in the winter. As shown in FIGURES 1 and 2, the apparatuscomprises generally a generator 5, a condenser 6, a receiver 7, anevaporator 8, an absorber 9 and a heat exchanger 10, all interconnectedto provide paths of flow for the circulation of refrigerant andabsorbent through the apparatus in closed circuits.

Evaporator 8 is a heat exchange coil which operates as an evaporatorduring the cooling cycle and as a heater during the heating cycle. Forpurposes of explanation it will be referred to as an evaporator.

As shown in FIGURE 2, a unit casing 31 has partitions 13, 15, and 17which divide the interior of the casing into a first compartment and asecond compartment. The first compartment contains the receiver 7, theevaporator 8, an evaporator fan 19 and a motor 21 for driving theevaporator fan through a belt 23. Air to be conditioned flows from theconditioned space into the casing through evaporator 8, then through fan19 which discharges the air from casing 11 to the conditioned space.

The second compartment in the casing 11 contains the generator 5, theconder er 6, the absorber 9, and a motor driven fan 25. Fan 25 forcesair from the second compartment of casing 11 thus drawing in air throughcondenser 6 and absorber 9 to cool the same. The generator receives airfrom the second compartment of casing 11 and discharges flue gas at apoint just below fan 25.

Cooling cycle The operation of the apparatus will first be describedwith reference to the cooling cycle.

Generator is heated by a burner 12 to vaporize refrigerant from theabsorbent. Burner 12 receives gas from a source 14. A pressure regulator16 reduces the pressure to the desired pressure. A relatively smallsolenoid gas valve 18 provides for flow of gas for low capacityoperation as for instance of full capacity. A relatively larger solenoidvalve 20 provides for a greater flow of gas or 75% of full capacityoperation so that when both valves are open the system operates at fullcapacity. A pilot 22 burns continuously for lighting the burner 12. Asafety pilot thermostatic switch 24 is provided to prevent start ingoperation if the pilot is not burning.

A high pressure switch 26 senses pressure in the generator 5 andterminates operation when the pressure in the generator exceeds apredetermined value due to some malfunction.

Refrigerant vapor produced in the generator 5 passes to a threewaysolenoid valve 28 which in its normally closed position passes the vaporto a conduit 30 which conducts the vapor to a condenser 6 whichtransfers heat to an air stream as will be described more fully.

From condenser 6, condensed refrigerant flows through conduit 32 to asolenoid operated valve 34. During cooling operation valve 34 is openand conducts refrigerant liquid to a receiver 7. A plurality of conduits36, 37, 38, and 39 conduct refrigerant liquid from receiver 7 toevaporator 8. Conduits 36, 37, 38 and 39 are spaced vertically so thatas the level rises in receiver 7, additional conduits conductrefrigerant liquid to the evaporator.

Evaporator 8 has a supply header 40 and a return header 42. A firstvertical row of horizontal tubes 43 extend between headers 40 and 42 anda second vertical row of horizontal tubes 44 extend between headers 40and 42. Heat transfer fins 45 are secured to the tubes 43 and 44.

As shown in FIGURES 3 and 4, the refrigerant liquid flowing in conduit39 is discharged into a first tube 43 from which it flows into a tray 47in header 42. The refrigerant vapor generated during the passage of therefrigerant through the first tube 43 passes downwardly through header42.

Refrigerant liquid in tray 47 passes in a return path through a tube 44into a tray 49 having a dam 5t). Refrigerant vapor generated in tube 44passes downwardly through header 4%) and the remaining refrigerantliquid flows through drain hole 51 in tray 49 to the next lower tray 52Which is similar to tray 49 except that the drain hole 53 is on theopposite side of dam 50. From this lower tray 52 the refrigerant liquidflows through a tube 44 to a tray 47 and thence through a tube 43 totray 52. If any refrigerant liquid remains after passing through thecircuit of four tubes, it flows through hole 53 into the next lowercircuit of four tubes.

Conduits 36, 37 and 38 each supply a circuit of four tubes in a mannersimilar to that described with reference to tube 39.

A low temperature thermostatic switch 55 opens when the temperature goesbelow 35 F.

The refrigerant vapor in headers 4i; and 42 flows into conduit 56 andthrough a normally open solenoid valve 57 of the pivoted vane type whichis open during the cooling cycle. From valve 57 the refrigerant vaporflows through conduit 58 into the supply header 6{) of absorber 9.

The previously described flow of refrigerant vapor from the generator 5is effective in maintaining a concentrated solution of absorbent in thegenerator 5. This concentrated absorbent solution flows from generator 5through conduit 61 to heat exchanger it? in which it exchanges heat withdilute solution flowing from the absorber 9 to the generator 5. Thecooled concentrated solution flows from heat exchanger 19 throughconduit 62 to header 66 of absorber 9.

The absorbent solution in header overflows into absorber tubes 63 andflows in a film down the inside surfaces thereof. The refrigerant vaporalso flows downward ly in absorber tubes 63 and is absorbed by the filmof absorbent on the inside surface of the tubes. Heat transfer fins 64are secured on the tubes 63 and is old and well known. Fan 25 draws airthrough the absorber 9 to remove heat therefrom.

The solution flows from tubes 63 into a return header 65 from which itflows successively through conduit 66, conduit 58, valve 57 and intoconduit 56. From conduit 56 the solution flows through conduit 67 topump 68. The solution from the discharge of pump 63 flows in partthrough conduit 69 into conduit 62 and to the absorber 9 and in partthrough heat exchanger 16": and thence through conduit 70 into the lowerportion of generator 5 to be reconcentrated.

Solution concentration is reduced as the load is reduced so thatdilution of the absorbent solution is not necessary when the machine isshut off after low load operation. If there is a power failure, motors21 and 27 of fans 19 and 25 stop, solution pump 63 stops and gas valves18 and 20 close. Also refrigerant liquid valve 34 closes. Refrigerantliquid flows from reservoir 7 into the evaporator 8 and thence intoconduits 56 and 67 to dilute the solution draining out of the absorber 9and thus prevent solidification of solution in these conduits.

The concentrated solution in conduit 62 and in heat exchanger it drainsby gravity through conduit 70 to the generator 5.

Heating cycle During the heating cycle valve 34 is tie-energized andtherefore in closed position. The condenser 6 is exposed to outsidetemperature which is usually low during the heating cycle with theresult that refrigerant vapor condenses therein with the result that alow pressure is created. The pressure in generator 5 is greater than thepressure in condenser 6, and therefore solution fiows through con duit72 from the generator 5 to the condenser 6 to fill the condenser withsolution. This action occurs after the solution has been diluted withrefrigerant from the receiver 7, and therefore the solution will notsolidify at normal winter temperatures.

During the heating cycle valve 28 is open between the generator 5 andconduit 56 to pass steam to conduit 56. From conduit 56 the steam flowsto evaporator headers 40 and 42 and thence to evaporator tubes 43 and44. It is thus seen that evaporator 8 operates as a heating coil to heatthe air of the conditioned space. The steam condensate flows downwardlythrough headers 40 and 42 via trays 47, 49, and 52 and thence intoconduit 56 from which it flows successively to conduit 67, pump 68, heatexchanger 10, conduit 70 and generator 5.

With valve 57 closed and absorber 9 exposed to a low outside ambienttemperature, condensation of vapor takes place in the absorber 9 and alow pressure is created with the result that absorbent solution flowsthrough conduit 62 to fill the absorber 9 with solution thus preventingfreezing in the absorber 9'. This action occurs after the solution hasbeen diluted with refrigerant from the re- 6 ceiver 7, and therefore thesolution will not solidify at normal winter temperatures.

If for some reason the pilot 22 should become extinguished in freezingweather, the condensate returning to the concentrator via conduit 67,pump 68, heat exchanger "iii and conduit 76 might freeze in spite of thefact that these passageways are insulated. To prevent this we constructthe solenoid valve 57 in a particular manner as will now be described.The blade 73 has a pivot 74 which is offset with respect to the axis ofconduit 56 with the result that a column of liquid in conduit 58 wouldact against a larger area with a force tending to open the vane 73 andagainst a smaller area with a force tending to hold the vane 725 closed.The solenoid is provided with insutlicient power to hold the vane 73 inclosed position against the force of the column of liquid in theabsorber 9 when the pressures of the evaporator and condenser decreasewith temperature due to loss of heat from pilot 22. The solutionreleased from absorber 9 will force the refrigerant liquid in conduit67, pump 63, heat exchanger it; and conduit 79 into the generator 5 andmix with any remaining liquid refrigerant thereby preventing destructivefreezing in these spaces.

Controls The control system will now be described with reference toFIGURE 5. A source of alternating current indicated by lines L1 and L2powers the controls. A rectifier 5:2- furnishes a source of directcurrent for the solenoid valves 28, 3d, and 57. A transformer 59furnishes reduced voltage for some controls.

A selective controller 76 is preferably mounted in the unit at alocation where it is exposed to the temperature of the space conditionedby the unit. A heating and cooling selector has a heating switch 77 anda cooling switch 78.

When switches 77 and 78 are both open, valves 23, 34, and 57 aretie-energized; the evaporator fan motor 21, the absorber-condenser fanmotor 27, and the pump 68 are de-energized, and gas valves 13 and 20 areclosed.

Heating control Let us assume now that it is desired to operate the unitfor heating and that the switch 77 is closed. This energizes the heatingrelay 79 provided that thermostat 80 in the absorber 9 senses atemperature below F. The

purpose of thermostat 80 is to prevent switching immedi ately fromcooling to heating with the attendant risk of solidifying theconcentrated solution in the absorber 9. Energization of the heatingrelay 79 closes contact 81 to energize solenoid valve 23 and solenoidvalve 57. Contacts 82, S3 and 84 are also closed so that when theheating thermostat 8S closes and demands heat, the gas valves 18 and 20are energized to open position, and the evaporator fan solenoid 86 isenergized to close contact 87 and start the evaporator fan motor 21.

There are certain safety devices which will prevent the gas valves 18and 26 from being energized to open position. The safety pilotthermostat 24 prevents energization of the gas valves if the pilot 22;is not burning. The high pressure switch 26 also prevents energizationif the pressure in the generator 5 is excessive. The low temperaturethermostat 55 in the evaporator opens and prevents operation when thetemperature of the evaporator is below 35 F. The high temperaturethermostat S9 in the generator 5 opens above 300 F. and de-energizes gasvalves 18 and 26 to closed position.

Cooling control Let us assume now that it is desired to operate the unitfor cooling and that switch '78 is closed. This energizes cooling relay9% which loses contact 92 and also contact 3 to energize valve 34 toopen position for flow of refrigerant liquid from condenser 6 toreceiver 7. If the temperature of the conditioned space rises slightlyabove the desired predetermined temperature, cooling thermostat 9icloses contact 95 to energize absorber condenser fan relay 96 whichcloses absorber condenser fan contact 97 to energize pump 68, relay 98,and the absorber condenser fan motor 27.

Energization of relay 98 closes contacts 99 and 105. With switch 95 andcontact 99 closed, gas valve .20 is energized to open position and lowcapacity cooling operation is obtained.

If the temperature of the conditioned space rises further above thedesired predetermined temperature, cooling thermostat 94 closes switch100 and gas valve 18 is energized to open position to operate the unitat full capacity. As the temperature falls toward the desiredpredetermined temperature gas valve 18 is first tie-energized to reducethe operation to low capacity and when the conditioned space reaches thedesired predetermined temperature "as valve 20 is de-energized toterminate the cooling operation.

A switch 101 may be in the position shown to operate the evaporator fanwhen the system is operating on the cooling cycle. If it is desired tooperate the evaporator fan when the unit is on the cooling cycle but notoperating, switch 101 may be moved to contact .102 to energize theevaporator fan motor 21 in order to circulate the air in the conditionedspace.

The absorber condenser fan motor 27 has a thermostat 103 in series withthe motor Winding 04 and the relay 98. If the temperature of the motor27 exceeds a predetermined value, thermostat 103 opens to de-energizethe motor winding 104 and de-energize relay 98 which causes contacts 99and 165 to open and de-energize gas valves 18 and 20 into closedposition.

Absorbent compositions of the invention Referring now to FIGURE 6, thefour curves marked LiBr 60%, 65%, and 68% by weight, and LiBrcrystallization line, illustrate the fact that it is impractical tooperate an absorption refrigeration process at temperatures above about125 F. with absorption refrigerating machines which employ lithiumbromide and water solutions as the refrigerant-absorbent combination andwhich must maintain refrigerating temperatures of about 40 F. in theevaporator.

To maintain an evaporator temperature of about 40 F., it is necessary tohave a vapor pressure of about 6 mm. Hg absolute, which is theapproximate vapor pres sure of water at 40 F. As hereinabove explained,for air conditioning equipment, the absorbent composition must be ableto maintain a vapor pressure less than that of water at 40 F. If oneattempts to operate with an absorber having a temperature as high as 125F. with aqueous solutions of lithium bromide, it can be seen from FIGURE6 that the operation would be very close to the crystallization line.This is impractical since crystallization resulting in high viscosityand freezing of the solution or clogging of the apparatus is very likelyto occur.

Referring again to FIGURE 6, the curves marked LiI Glycol, 80% by weightand LiI Glycol, 84% by weight, and their accompanying curve markedCrystallization Line, illustrate the fact that these examples of our newand improved absorbent composition are capable of maintaining a vaporpressure less than that of water at 40 F. even when the temperature ofthe absorbent solution in the absorber is as high as 150 F. and above.For convenience, the ingredients of these particular examples of ourimproved absorbent and the ratio of the weight of lithium iodide toethylene glycol of 7 is also marked on FIGURE 6. The vapor pressurecurves for these two compositions is fairly typical of the vaporpressure curves for the other proportions of lithium iodide, ethyleneglycol and water. The absorptive ability of our new and improvedabsorbent composition at such high temperatures, makes practical thedissipation of heat directly to an air sink.

In interpreting curves such as shown in' FIGURE 6 and the other figuresin this application, the following principle, which was published andwell known long prior to our work, should be kept in mind. The greaterthe number of molecules (moles) dissolved in the absorbent solution, thegreater is the lowering of the vapor pressure of the absorbent solution.The lower the vapor pressure of the absorbent solution, the greater isthe absorbent capacity of afiinity of the absorbent solution for the refrigerant vapors. Consequently, the molecular weight of an absorbentmust be considered as much as its weight percent or concentration in theabsorbent solution. For example, the molecular weight of lithium bromideis about 87 and that of lithium iodide about 134. Thus, a 65 weightpercent lithium bromide water solution contains more molecules ofabsorbent that a 72 Weight percent lithium iodide water solution. Thisis one of the reasons why, prior to our work, lithium bromide was usedcommercially whereas lithium iodide was not.

In searching for some refrigerant-absorbent combination that mightpermit an absorption refrigeration process to dissipate heat directly toair as a heat sink, we selected water for the refrigerant because of itsknown advantages, and elected to test with Water many differentabsorbents including some previously tested and discarded by others onthe basis of the data previously obtained.

The relative merits of aqueous solutions of various salts in providingthe desired vapor pressure lowering were considered in ourinvestigation. Lithium iodide was considered during this phase of theinvestigation although it was known to be of little value by itself inaqueous solution, because its molar solubility is lower than that oflithium bromide at moderate temperatures.

An investigation was also made of a lithium bromideethylene glycol-water(LiBr-C H O -H O) system. Results of these tests are shown in FIGURE 8,a triangular coordinate chart showing isothermal crystallization curvesat 77 F. and 150 F. It was found that this system produced lower totalvapor pressures of water above the solutions at lower concentrations oflithium bromide in the glycol and water could be used at highertemperatures without danger of crystallization. However, the viscosityof such. solutions was very high even. at 150 F. and for this reasonthis system was not practical.

An investigation was also made on the lithium iodide, ethylene glycoland water (LiI-C H O -H O) system. The results of this investigation areshown in FIGURE 9, a triangular coordinate chart showing isothermalcrystallization curves at 80 F., F. and F. The test at 150 F. was notextended to the composition having no water; however, the reasonableassumption Was made that the curve extends along dotted line 12 and thatthe 120 F. and the 80 F. curves follow substantially the same pattern.These curves show that the solubility of lithium iodide in ethyleneglycol-water solutions is unexpectedly greater than the solubility oflithium iodide in water. The curves also indicate a higher solubility oflithium iodide in pure ethylene glycol than for lithium iodide in purewater.

It is evident from a comparison of FIGURE 8 and FIGURE 9 that theresults of the crystallization tests on the system LiI-C H O -H O shownin FIGURE 9 are significantly different from what could be expected fromthe previously obtained results on the system LiBr-C H O -H O shown inFIGURE 8. Also, the viscosity of the system LiI-C H O -H O was found notto be large at elevated temperatures.

As shown by the results in FIGURE 9, unusual ability to operate at highheat sink temperatures is possessed by absorption systems comprisingaqueous solutions of a mixture of lithium iodide and ethylene glycol inwhich the weight ratio of lithium iodide/ethylene glycol is betweenabout 2.5 and 13. This is shown by the 150 F. and 120 F. crystallizationcurves in FIGURE 9. The portions of these curves between the lines 2.5and 13 have an unexpected slope between the weight ratios of lithiumiodide/ ethylene glycol of between 2.5 and 13. It is this unexpectedslope which demonstrates the exceptional ability of the absorbentcompositions of the invention to permit operation with an absorptionrefrigeration system employing a high temperature heat sink, such as onewhich operates on air cooled heat exchange basis. It is preferred toemploy solutions having a weight ratio of lithium iodide/ethylene glycolof between about 2.5 and 7 or most esirably between about 3 and 5.

The following examples are illustrative of typical absorbentcompositions falling within the scope of our invention. It will beunderstood that others may readily be prepared in the light of thedisclosures provided herein. in the examples which follow, thecompositions are prepared by adding sufiicient amounts of the componentsto provide the indicated weight percent.

It should be understood that small amounts of corrosion inhibitingsubstances may be added to these absorbent compositions in accordancewith the usual practice in the art.

While the absorption refrigeration system of the invention has beendisclosed in conjunction with a preferred absorption refrigerationapparatus, it should be understood that the absorption refrigerationcompositions and methods of the invention may be employed with anabsorption refrigeration system of a diflerent design, such as thoseconventionally employed in absorption refrigeration.

The absorption refrigeration apparatus disclosed herein does not per seconstitute a part of the present invention. Such apparatus is theinvention of David G. Peckham and Robert G. Miner and is claimed intheir US. patent application, Ser. No. 509,145, filed Nov. 22, 1965.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to witohut departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

What is claimed is:

1. Absorption refrigeration system comprising, in combination, anabsorbent refrigeration apparatus comprising a generator, a condenser,an evaporator, and an absorber connected to form a refrigeration unitwith an absorbent composition in said apparatus, said absorbentcomposition consisting essentially of a solution of lithium iodide andethylene glycol in water, the weight of lithium iodide being about 2.5to 13 times the weight of ethylene glycol and in which the weight ofwater is about 5% to 38% of the weight of the solution.

2. Absorption refrigeration system according to claim 1 in which thelithium iodide is about 2.5 to 7 times the weight of ethylene glycol.

3. Absorption refrigeration system according to claim 1 in which thelithium iodide is about 3 to 5 times the weight of ethylene glycol.

4. An absorption refrigeration system according to claim 1 in which theweight of water is 16% to 27% of the weight of the solution.

5. A method of producing refrigeration comprising the steps of passingan absorbent solution consisting essentially of lithium iodide andethylene glycol in Water, the weight of lithium iodide being about 2.5times to 13 times the weight of ethylene glycol, to a heating zone togenerate water vapor and concentrate said solution, passing the watervapor to a condensing zone in which the water vapor is condensed toliquid water by transferring heat to a heat sink, passing said liquidWater to an evaporating zone, passing said absorbent solution to anabsorbing zone in fluid communication with said evaporating zone andtransferring heat from said absorbing Zone to a heat sink whilemaintaining said absorbent solution in a liquid state at temperatures ofabout 130 F. and above to maintain an evaporator temperature of about 40F. and passing said absorbent solution from said absorbing zone to saidheating zone to be reconcentrated.

6. A method according to claim 5 in which the absorbent solutionconsists essentially of lithium iodide and ethylene glycol in water, theweight of lithium iodide being about 2.5 to 7 times the Weight ofethylene glycol.

7. A method according to claim 5 in which the absorbent solutionconsists essentially of lithium iodide and ethylene glycol in water, theweight of lithium iodide being about 3 to 5 times the weight of ethyleneglycol.

OTHER REFERENCES Hainsworth, Refrigerating Engineering; September 1944,Vol. 48, pp. 201-205, TP 490, A 52, 252-67.

ROBERT A. OLEARY, Primary Examiner.

LLOYD L. KING, Examiner.

